Apparatus for the treatment by metallic ions of aqueous liquids

ABSTRACT

A DEVICE FOR LIQUID PURIFICATION INCLUDES A VAT PROVIDED WITH METALLIC ELECTRODES AND CONNECTED TO A CIRCULATING PUMP AND TO A FILTER CONTAINING AT LEAST ONE FILTERING LAYER OF LOW GRANULOMETRY BUILT UP FROM ACCUMULATION OF FLUOCCULATES. THE DEVICE IS PARTICULARLY SUITED FOR WATER TREATMENT.

5:91. 10, 1974 P CASANQVAS ETAL 3,835,018

APPARATUS FDR THE TREATMENT BY METALLIC IONS 0F AQUEOUSLIQUIDS I Original Filed oCt. 28, 1970 Fial nitecl- States Patent US. Cl. 204-228 5 Claims ABSTRACT OF THE DISCLOSURE A device for liquid purification includes a vat provided with metallic electrodes and connected to a circulating pump and to a filter containing at least one filtering layer of low granulometry built up from accumulation of flocculates. The device is particularly suited for water treatment.

This is a divisional of application Ser. No. 84,861 filed Oct. '28, 1970.

It is well known that in purification of aqueous liquids, and more particularly water, there are two types of underisable elements which are, on one hand, impurities in suspension and, on the other hand, the dissolved impurities. The impurities in suspension are in the form of precipitates or colloids, and the dissolved impurities are in the ionic state, that is they have extremely small sizes and are electrically charged.

' In some purifying processes utilized until now to eliminate these impurities, fiuocculation processes have been utilized; they consist of introducing a reactant into the liquid to create colloids with adsorption properties, said colloids forming a group then ensuring the flocculation and enclosing simultaneously the impurities in suspension. The flocculation provide large sized particles which can be separated from the liquid, either by decantation or by filtering or a combination of these two processes.

To create said flocculation, metallic salts are utilized, such as the aluminum sulphate Al(SO or ferrous chloride FeCl which are very soluble in water and dissociate giving off their metallic ions; these ions in combination with the hydroxyl ions (OH) contained in the water form a corresponding metallic hydroxide that shows adsorption and then flocculation properties. The process is similar for all flocculents with chloride, nitrate or sulphate basis which, upon their reaction, give off the cor responding anion that is not useful for the flocculation and which has the disadvantage, when present, to cause an acidification of the liquid considering that this anion always comes from strong acid salts, and consequently the pH of the liquid has to be adjusted to a correct value.

Besides, often the pH of the liquid has to be adjusted to' provide flocculation, and especially it is well known that the alumina hydrate coagulates well only when the pH of the solution is lower than 7.4 or higher than 8.5. When ferrous hydroxide is utilized as a coagulant, it is first necessary to adjust the pH to a value higher than 6.

It has also been noticed that when using chemical reactants it is necessary to introduce said reactant in rather large quantities, and at least drop by drop, resulting in a dissociation between the metallic ions and the anions in areas of small surface active. This causes a rapid formation of the hydroxide and an increase thereof in a low volume. There results consequently a poor adsorption Patented Sept. 10, 1974 power, and, to properly moreover produce the flocculate requires a stirring of the liquid.

From the invention, all above mentioned disadvantages are eliminated because anions (nitrates, sulphates or chlorides) are not introduced into the liquid to be treated and also because the metallic ions are evenly introduced into the liquid, exactly as if they were introduced one by one, whereby the resulting active surface is considerable for a determined mass of metallic ions introduced into the liquid under treatment.

According to the invention, the process for the electrolytic treatment an aqueous liquid is characterized in that a scattered emission of metallic ions is produced in the aqueous liquid from metallic electrodes submitted to the action of an electric current, the quantity of which when applied to said electrodes determines the quantity of ions sent out, whereby some of the metallic ions sent out are combined with hydroxyl ions which are in the liquid, thus creating colloidal particles having a high adsorbing power and causing a fine flocculation, and in that the fine flocculate is continuously retained during formation in the form of a porous filtering mass which is traversed by the liquid still comprising metallic ions and also in that the quantity of metallic ions which is electrically produced is selected to allow penetration of metallic ions through the porous mass of and drawing away therefrom by the treated liquid, whereby the treated liquid comprises some free metallic ions raising the resulting electrical potential of the treated liquid in comparison with the potential of the liquid before the metallic ions emission.

According to another important characteristic of the invention, the porous mass of fiocculate is constituted by impregnating with the nascent flocculate a filtering mass with low granulometry, the flocculate being retained in said filtering mass until the same shows a loss of pressure substantially quadruple of the loss of pressure noticed on beginning of treatment, whereby said filtering mass impregneted with the flocculate forms a self-regulating buffer of the quantity of free metal ions having not caused a flocculation and which are drawn away from said porous mass of flocculate to maintain a high electri cal potential of the treated liquid.

From the above mentioned process, very numerous treatments can be made with a rare efliciency. Actually, according to the nature of the particular constitutive metal utilized for the electrodes from which the metallic ions are emitted, the result which is obtained for the liquids, especially water, treated by the process show that said liquids are cleared out of all foreign elements that they contained. Besides they show bactericidal and algicidal properties especially when this metal is copper, deodorant and desalinizing properties when the metal is iron, or some other properties such as a catalytic action allowing the development of yeast when the treatment is applied to distillery liquids, the acidification of which is considerably decreased.

Upon practice of the invention there has also been surprinsingly noticed that a very eflicient purification of the radio-active waters could be obtained. This constitutes a very important embodiment of the process of the invention.

Other characteristics of the invention are shown in the following detailed description.

Embodiments of the invention are shown by way of non-restrictive examples in the accompanying drawing.

FIG. 1 is a diagrammatic view of a close-circuit installation for treatment embodying the process of the invention.

FIG. 2 is a diagrammatic view of a treatment at illustrating a particular characteristic of the invention.

FIG. 3 is a diagram of a colloidal particle formed from the ionic emission, according to the process of the invention.

With reference to FIG. 1, a vat or tank 1 contains a liquid intended to be treated, for example water to be purified. A conduit 2 brings the waters to a prefilter 3, and a circulating pump 4 is connected through a discharge pipe 5 to a treatment vat 6 containing metallic electrodes supplied with electric current. The outlet of the treatment vat 6 is connected by a part 7 to a upper part 8 of a filter 9. The inside of filter 9 is provided with a load 10 of filtering material composed for example of flint and which is arranged in two layers 10a, 10b.

In the case of the treatment of a water, for example swimming-pool water, the layer 10a is composed of granules of about 0.4 mm. in diameter and the layer 10b of granules of 1.4 mm. in diameter, said layer 10a filling the two thirds of the filter whereas the layer 1012 fills only one third. The whole of the filtering mass is installed on a grate 10d to leave an empty space 11 at the filter base. The filtered waters are afterwards brought back into the vat or tank 1 through a pipe 12.

FIG. 2 shows in a diagrammatic way, but in an enlarged view, how the treatment vat 6 may be constituted. This treatment vat has an inlet cavity 13 connected to the pipe 5 and an outlet cavity 14 connected to the pipe 7. Between said two cavities 13 and 14 are placed in an alternate way, metallic electrodes 15 and 16 respectively connected to conductors 17 and 18 leading to an electric supply source 19 which can be either direct or alternating, or only pulsed as it is generally preferred. It is thus possible to utilize a current directly supplied from an alternating means of which the voltage is lowered to about ten volts, the current is then rectified whereby alternances of a same polarity are applied to each of the electrodes, then the connection between the source terminals and the electrodes may be cyclically reversed in order to depolarize the eiectrodes after a certain period of operation.

In the example represented, only three electrodes are shown but it is obvious that any number of electrodes can be utilized.

To obtain a correct working of the invention, it is important that the release of metallic ions be very uniform. For this purpose, uniform liquid circulation between the electrodes of opposite polarity is provided. To obtain this result, a first means consists of controlling the shape of the inlet cavity 13 and outlet cavity 14 in order that the liquid be distributed equally into the channels 20 which are delimited between the electrodes. Several mechanical means can be considered to obtain this result, for instance the inlet and outlet walls of the treatment vat can be substantially shaped in the form of a parabola or a frustoconical surface end besides, deflector elements 21 can be provided at least above channels 20 whereby the flow of liquid in these channels be the same.

In addition and still for obtaining a uniform treatment, and this is especially important in critical treatments requiring a complete embodiment of the invention, for example when radio-active waters are to be treated, the far end electrodes, which are the electrodes 15 in the represented example, are connected to the walls of the vat 6 by filling elements 22 preventing the liquid from flowing between said electrodes and walls, since the liquid which would flow through this way would not be treated in the same manner as the one flowing between two electrodes of opposite polarities.

With the above described means and especially with the particular fitting of the treatment vat 6, the liquid circulating between electrodes 15 and 16 is charged with metallic ions. It has been determined that said ions form hydroxides, in the presence of the hydroxyl ions of the solution, for example copper hydroxides if the electrodes are made of copper. As schematically shown in FIG. 3, these copper hydroxides, of a Cu(OH) formula, form a primary particle 23 which is surrounded by a first layer 24 formed of adsorbed ions, then by a second layer 25 formed of ions electrostatically attracted, this complex particle corresponding to a colloidal status.

The potential difference existing between the outer side of the primary particle 23 and the first layer of the solu-. tion is called Nerst potential while the potential difference existing between the first and the second layer is called Stern potential. The electro-kinetic potential of the colloidal particle is the difference of potential existing between the outer side of the second layer 25 and the liquid in which is maintained the colloidal particle. Said potential can be measured and the value thereof is determined by the Choluchowski equation, that is:

in which 1 is the liquid viscosity, ,0; the migration speed of the colloidal particle, H the potential gradient and D a dielectric constant. The electrokinetic potential then defines the possibility of flocculation.

Since the colloidal particles are at the electrokinetic potential, electric forces of repulsion exist therebetween because these particles are electrically charged and of the electro-kinetie potential same sign, but there also exist mechanical forces of attraction which are known under the name of van der Waals forces which vary inversely with the seventh power of the distance separating the particles.

Because of both the repulsion forces existing due to electrical charges of colloidal particles created from the ionic emission from the electrodes and the van der Waals attraction forces, it is obvious that it is the resultant of these two forces which determines the possibility for two particles to meet, coagulate and then to fiocculate.

Since there is in the liquid to be treated an homogeneous distribution of the released ions obtained upon the embodiment of the invention the emission of metallic ions is made possible from all the surface of the electrodes, then for a determined mass of metal extracted from each anode, the active surface of the particles is considerable and out of proportion with the surface obtained from a metallic salt.

It can be calculated that the particles which are created from the ionic emission are in the range of 0.5 1 to 1 my. and consequently they present a considerable surfacemass ratio since the calculation shows also that one cm. of particle divided into cubes of 1 m per side, would show an active surface of 6600 m.

For the reasons explained above and the great dispersion of the colloidal particles formed from ions emitted in the liquid, the formation of flocculate i fine and scattered. The result thereof is that the flocculates under formation have themselves great adsorption properties. 7

Because of the line and scattered formation thereof, the flocculate penetrates into the filtering layer 10a of the filter and progressively, in the course of the treatment embodiment, saturates the whole depth k of the filtering mass having a low granulometry, this low granulometry being preferred because of the small size of the fiocculates formed, whereby the filter is progessively filled with a porous mass of flocculate so that the liquid added with flocculate while going through the porous mass progressively cooperates to its formation.

When put into practice and for a filter presenting upon beginning of utilization a loss of pressure of 0.5 bar, the flocculate impregnating the filter is left to develop until the loss of pressure in the filter has reached from 1.5 to 2 bars. Then the filtering mass 10 is washed to remove the flocculate in excess and the treatment starts again in the same way.

As it appears from above, by embodying the process of the invention, the totality of the filtering mass is used as a filter since this whole mass is progressively saturated by the fine flocculate, contrarily to what occurs when the filters are utilized to retain fiocculates formed by known methods. In that latter case, the filter constitutes a barrier on the top of which a cake of flocculate is formed without penetrating into the filtering material which has not, then an active action regarding the purification process.

If desired, the filter 9 can be replaced by a decanter but of course in that case the circulating speed of the liquid must be considerably decreased in order that the flocculate which is retained in the decanter and which has to be saturated by the liquid under treatment will develop as a group of thick fiocculates which must not be carried away. This process is therefore sometimes advantageous for the treatment of very large quantities of water and also when combined to a subsequent filtering in a filter of the type of the one described above because then the fine floculates of the decanter can advantageously be carried to the filter to ensure the saturation and consequently the activity thereof.

The quantity of active residual ions which remains in the liquid after running through the filter is an important feature of the present invention and said active residual ions are more often desired in the treatment process because they provide a raise in the potential of the treated liquid. As an example a water added with copper of 90 gamma of thousandths of milligrams/ liter has a voltage raised from 60 to 120 millivolts, which considerably causes favorable complementary treatment effects, especially microbicidal and algicidal elfects. That is explained by the fact that the metallic ions, especially the ions of copper and silver, gold, platinum, etc., show avidity towards proteinic substances of bacteria, various germs and virus: the change in electrical potential of the medium resulting from the presence of ions, acts moreover as a depressive agent of the superficial voltage which in some cases causes the bursting or the degeneration of microbial cells.

As already mentioned above, the process of the invention presents a very particular activity when embodied for the decontamination of radio-active water. In fact it has been checked that practically all the radio-active isotopes, contained in contaminated water, were retained. It has been especially checked for the following elements.

Elements Retention (percent Rhodium u} 100 The invention is not restricted to the embodiments shown and described in detail, for various modifications thereof can moreover be applied to it without departing from the scope of the invention. In particular, though the invention has been described with reference to water treatment, in close circuit, from a vat, it is obvious that it can be embodied, in a similar way, for a treatment in open circuit, the treated water could be rendered drinkable for human consumption or regenerated for an industrial treatment or only treated and returned to the river.

What we claim: 1. A device for treating liquids containing impurities comprising:

means to form fine flocculates from the impurities of said liquid comprising a chamber having inlet means and outlet means through which the liquid flows and means to effect uniformly scattered emission of ions of a single metal through the liquid, said latter means comprising positive and negative metal electrodes of a single metal in said chamber, means to pass the liquid in an equally distributed manner between said metal electrodes, and a variable power source having two poles each of which is connected to a said positive or negative metal electrode; and

means to retain therewithin the fine fiocculates, said means having its upper portion connected to said chamber at the output of said chamber to retain the fine flocculates within said retaining means in the form of a porous mass whereby a porous and active mass filter is formed for subsequently formed fine fiocculates.

2. A device as set forth in Claim 1, wherein the means to retain the fine flocculates comprise a filter con taining at least one filtering layer of small size particles, whereby said layer is progressively impregnated along its entire depth by the fine flocculates under formation.

3. A device as set forth in Claim 1, wherein the vat is provided with means for deflecting the liquids toward the metal electrodes whereby the liquid passes uniformly between said electrodes.

4. A device as set forth in Claim 1, wherein one of said positive or negative metal electrodes is positioned immediately against the wall of the chamber and is connected thereto through isolating and electrically insulating means, whereby no liquid can flow between the wall of the chamber and said electrode so positioned.

5. A device in accordance with Claim 1 wherein said power source comprises means to raise potential of the liquid whereby the filtered liquid has an elevated electrical potential effective to provide biocidal activity.

References Cited UNITED STATES PATENTS 1,219,333 3/1917 Kynaston 204240 3,222,268 12/ 1965 Clauss et al 204238 892,486 7/1908 Woolf 204240 X 2,658,033 11/1953 Ferris 204152 3,405,050 10/1968 Bovard et al. 204240 3,691,050 9/1972 Sayre 204276 X 3,092,566 6/1963 Negus 204152 X JOHN H. MACK, Primary Examiner D. R. VALENTINE, Assistant Examiner U.S. Cl. X.R. 204235, 276 

